Within the context of a program directed at determination of the specific actions of insulin, glucocorticoids and prolactin in the regulation of mammary metabolism; and, at evaluation of the metabolic changes occurring in extramammary tissues during lactation and the regulation of these, a series of studies will be undertaken as follows: 1) Determination of hormone actions upon and sites of cyclic AMP action in rat mammary tissue; 2) Determination of acute actions of insulin upon rat mammary cell metabolism and long term actions of insulin in mammary cell maintenance in vivo; 3) Determination of primary regulatory and rate-limiting enzymes in mammary tissue and their role in the regulation of mammary metabolism and as sites of hormone action; 4) Characterization of metabolic changes in gastrointestinal, liver and adipose tissue during lactation and identification of the (hormonal) causes of these; and, 5) Identification of metabolic inefficiencies leading to less than optimal lactational efficiencies in rats and cows.